Tetrabromophthalic diester flame retardants and their production

ABSTRACT

In a process for producing a tetrabromophthalic diester composition, a liquid reaction mixture is prepared comprising tetrabromophthalic anhydride (TBPA), a C 2  to C 6  polyhydric aliphatic alcohol (PAA) and an alkylene oxide (AO) selected from the group consisting of ethylene oxide and propylene oxide, said reaction mixture being substantially free of an organic solvent. While agitating the reaction mixture, the temperature of the reaction mixture is raised to at least 50° C. to allow the TBPA to react with the PAA and AO to produce a diester composition. The reaction is terminated when the diester composition has an acid value equal to or less than 0.25 mg KOH/gm of the diester composition.

This application is a divisional of U.S. application Ser. No.12/980,469, filed Dec. 29, 2010, which application claims benefit under35 USC 119(e) of U.S. Prov. Appl. No. 61/292,988, filed Jan. 7, 2010,the disclosures of which are incorporated herein by reference.

This invention relates to tetrabromophthalic diester flame retardantsand their production.

BACKGROUND

Hydroxyl-terminated derivatives of tetrabromophthalic anhydride are wellknown flame retardants. Thus tetrabromophthalic anhydride (TBPA) has ahigh bromine content (68.9%), by which it or its derivatives can be usedto impart flame retardancy to a variety plastic systems, such aspolyurethanes and especially polyurethane foams. Particular examples ofcommercial flame retardants based on hydroxyl-terminated derivatives oftetrabromophthalic anhydride are PHT-DIOL supplied by ChemturaCorporation (a mixed ester of tetrabromophthalic anhydride withdiethylene glycol and propylene oxide) and SAYTEX RB-79 supplied byAlbemarle Corporation (a mixed ester of tetrabromophthalic anhydridewith diethylene glycol and propylene glycol).

Because diesterification of TBPA is difficult using conventionalesterification techniques, the art has turned to a method which involvesreacting TBPA with a polyhydric alcohol (e.g. glycols) to form ahalf-ester and, subsequently, reacting the half-ester with an alkyleneoxide such as propylene oxide or ethylene oxide to form the diester. Anexample of such a process is disclosed in U.S. Pat. No. 3,455,886, inwhich an anhydride is first reacted with a polyhydric alcohol at atemperature of 80 to 150° C. and, only when substantially all of theanhydride has reacted with the alcohol, is an epoxide added to thereaction mixture and the reaction to form the final diester completed ata temperature of 60 to 160° C.

More recently a single step, batch wise process for producingtetrabromophthalic diester compositions has been proposed in U.S. Pat.No. 5,332,859. This process comprises (a) preparing a first batch byreacting, in an inert organic solvent, normally toluene, at atemperature up to about 150° C., tetrabromophthalic anhydride (TBPA), aC₂ to C₆ polyhydric aliphatic alcohol (PAA) and an alkylene oxide (AO)selected from the group consisting of ethylene oxide and propyleneoxide, said reacting being in a PAA:AO:TBPA mole ratio of1.6-1.9:1.3-1.5:1, so as to obtain a reacted mixture including thetetrabromophthalic diester composition and the organic solvent; (b)recovering the organic solvent from the reaction mixture bydistillation; (c) analyzing the recovered organic solvent to determinethe level of its AO content; and (d) preparing a second batch byrepeating step (a) above wherein the organic solvent used includes therecovered organic solvent from the previous batch and wherein itsdetermined AO level is accounted for in achieving the PAA:AO:TBPA moleratio.

The diester product of the process of the '859 patent is a viscousliquid which becomes less viscous with increasing temperature.Typically, the product has a viscosity at 25° C. ranging from 80,000 to150,000 cps, which imposes significant problems in handling the productduring processing. As a result, formulators generally have to heat theproduct to move it through plant equipment. In addition, they addmodifiers to reduce the viscosity of their formulated products. It wouldtherefore be desirable to develop an improved single step process forproducing tetrabromophthalic diester compositions in which the viscosityof the product can be reduced.

According to the present invention, it has now been found that, byconducting the single step process of the '859 patent in the absence ofthe toluene solvent, a lower viscosity product can be produced. Even inthe absence of the toluene solvent, the remaining raw materials form asolution that is viscous but can be stirred. Therefore, the toluene isnot necessary for agitation purposes. By removing the toluene from theprocess entirely, the process step to distill and recover toluene fromthe product is also eliminated. Not only does this avoid the costsassociated with the toluene removal, but also having to remove tolueneat the end of the reaction appears to be important to the viscosity ofthe product. In particular, it is believed that holding the reactionproduct at toluene strip temperatures for an extended period results infurther reaction of any excess alkylene oxide and hence extension of thediol side chains. As the side chains get longer, increased chainentanglement is possible which results in higher viscosity at any giventemperature.

SUMMARY

In one aspect, the invention resides in a process for producing atetrabromophthalic diester composition, the process comprising:

-   (a) preparing a liquid reaction mixture comprising    tetrabromophthalic anhydride (TBPA), a C₂ to C₆ polyhydric aliphatic    alcohol (PAA) and a C₃ to C₈ alkylene oxide (AO), said reaction    mixture being substantially free of an organic solvent;-   (b) while agitating the reaction mixture, raising the temperature of    the reaction mixture to at least 50° C. and allowing the TBPA to    react with the PAA and AO to produce a diester composition; and-   (c) terminating the reaction when the diester composition has an    acid value equal to or less than 0.25 mg KOH/gm of diester    composition.

In one embodiment, the C₂ to C₆ polyhydric aliphatic alcohol (PAA)comprises diethylene glycol and the alkylene oxide (AO) comprisespropylene oxide.

Conveniently, the reaction mixture prepared in (a) has a PAA:TBPA moleratio of about 1 to about 2.5:1.

Conveniently, the reaction mixture prepared in (a) has an AO:TBPA moleratio of about 1.5 to about 2:1.

Conveniently, the reaction mixture also comprises potassium hydroxide inamount between about 0.001 to about 0.05 mole per mole of TBPA.

Conveniently, the reaction is terminated when the diester compositionhas an acid value between about 0.04 and about 0.10 mg KOH/gm of diestercomposition.

Conveniently, the diester composition has a viscosity of about 7,500 toabout 100,000 cps at 25° C.

Conveniently, the temperature of the reaction mixture is cooled during(b) so as to maintain said temperature at or below 120° C.

Conveniently, the process further comprises:

-   (d) after terminating the reaction, removing unreacted alkylene    oxide by evacuating the reaction mixture at a temperature of about    60 to about 90° C.

In a further aspect, the invention resides in a diester oftetrabromophthalic acid with a C₂ to C₆ polyhydric aliphatic alcohol(PAA) and a C₃ to C₈ alkylene oxide (AO) having a viscosity of about7,500 to about 50,000 cps at 25° C.

In yet a further aspect, the invention resides in the use of thetetrabromophthalic diester composition described herein in flameretardant polymer compositions, particularly those employingpolyurethanes.

DETAILED DESCRIPTION

Described herein is a diester diol of tetrabromophthalic acid, itsproduction and its use as a flame retardant particularly, but notexclusively, for use in polyurethanes and especially polyurethane foams.The present diester diol is the reaction product of tetrabromophthalicanhydride (TBPA), a C₂ to C₆ polyhydric aliphatic alcohol (PAA),preferably diethylene glycol, and a substituted or unsubstituted C₃ toC₈ alkylene oxide (AO), preferably propylene oxide. In one practicalembodiment, in which the PAA is diethylene glycol and the AO ispropylene oxide, the diester diol has the following formula:

where n is typically in the range from about 1 to about 5.

The present diester diol has a viscosity at 25° C. of about 7,500 toabout 100,000 cps, typically from about 7,500 to about 50,000 cps andespecially from about 15,000 to about 40,000 cps, making the lowerviscosity products suitable for use in foam applications that that havepreviously been excluded for equivalent materials with higher viscosity.In particular, in its low viscosity forms, the present diester diol ispourable at room temperature and can be pumped using standard machinepumps commonly used for spray polyurethane foam, flexible slab stock,flexible box pour, rigid discontinuous lamination panels, rigidcontinuous lamination panels, pour-in-place/molded applications; as wellas, adhesive applications.

The present diester diol is produced in a liquid phase process in whichtetrabromophthalic anhydride (TBPA) is reacted with both a C₂ to C₆polyhydric aliphatic alcohol (PAA) and an alkylene oxide (AO) in asingle stage and in the absence of an organic solvent, such as toluene.The process typically involves adding the TBPA to the PAA to form athick, but stirrable, slurry. Potassium hydroxide is then normally addedto the slurry partially to neutralize residual acid from the TBPA andpartly to act as a chain extension catalyst to control the overallmolecular weight and viscosity of the product. The AO is then added toslurry and the ingredients are blended together to form a homogeneousreaction mixture having the following molar composition:

-   -   PAA:TBPA=about 1 to about 2.5:1;    -   AO:TBPA=about 1.5 to about 2.0:1; and    -   KOH:TBPA=about 0.001 to about 0.05:1.

The alkylene oxide (AO) can be added in total at the beginning of thereaction, or it can be added in multiple stages, provided that at leasta portion of the overall AO is present at the beginning. For example, inone embodiment, about 20 to 35% of the AO is added at the beginning ofthe reaction and then after allowing a certain amount of reaction totake place, the remainder of the AO is added. In some instances eachaddition of the AO is gradual, e.g., over 0.2 to 5.0 hours, and in somecases, a period of time is allowed to elapse, often at elevatedtemperature between the first addition of a portion of the AO and thesecond addition of the remainder.

The amount of PAA added to the reaction mixture can be varied to adjustthe viscosity of the final diester diol, with higher values within thePAA:TBPA range given above resulting in lower viscosity products. Toproduce a low viscosity product (about 15,000 to about 50,000 cps at 25°C.), PAA:TBPA mole ratio is generally adjusted to be in the range ofabout 1.5 to about 2:1

The resultant reaction mixture is then heated under stirring to atemperature of at least 50° C., generally between about 60° C. and about65° C., to initiate the esterification reaction. Since the reaction isexothermic, the temperature may rise as the reaction proceeds and socooling is generally applied to the reaction mixture to retain thetemperature at or below 120° C. The reaction mixture is then maintainedat this temperature for about 2 hours to about 8 hours to complete thereaction. The reaction is terminated when the diester composition has anacid value equal to or less than 0.25 mg KOH/gm, generally between about0.04 and about 0.10 mg KOH/gm, of the diester composition. After thereaction has been terminated, residual propylene oxide is bled to ascrubber and the reaction mixture held under vacuum to remove volatiles.

The resultant diester diol of tetrabromophthalic acid can be used as aflame retardant for many different polymer resin systems such aspolystyrene, high-impact polystyrene (HIPS), poly(acrylonitrilebutadiene styrene) (ABS), polycarbonates (PC), PC-ABS blends,polyolefins, polyesters and/or polyamides and polyurethanes. Because ofits thermal stability, bromine content and reactivity, the product isparticularly useful as a flame retardant for polyurethanes andespecially polyurethane foams. In flame retarding polyurethanes, thepresent diester diol is used as a reactive additive and can be presentin the final formulated resin at levels of about 1% to as much as 55%.Preferably, the amounts range from 3 to 30% with a particularlypreferable amount ranging from 5 to 15%.

Although the present diester diol can be used alone to enhance the flameretardant properties of a polymer composition, it may in some cases bedesirable to blend the diester diol with other flame retardantmaterials. One particularly useful blend is with at least one hinderedphenolic antioxidant since such a blend not only offers flame retardancybut also anti-scorch/anti-discoloration properties. A suitable hinderedphenolic antioxidant is one in which the phenolic ring is substituted byan alkanoic acid alkyl ester group in which alkanoic acid moiety has inthe range of about 2 to about 4 carbon atoms and the alkyl group has inthe range of about 6 to about 16 carbon atoms. Specific examples of suchhindered phenolic compounds include ANOX 1315, ANOX 70, ANOX 330,NAUGARD 431, and NAUGARD BHT, all supplied by Chemtura Corporation.There are many other examples of phenolic antioxidants that areavailable from other suppliers as well. Typically the ratio of the diolester to the hindered phenolic antioxidant is in the range of about100:0.1 to about 100:1.

The invention will now be more particularly described with reference tothe following non-limiting Examples.

Example 1

240 grams (2.26 moles) of diethylene glycol (DEG) are loaded into a 1liter one-piece pressure reactor equipped with a stirrer and 640 grams(1.38 moles) of tetrabromophthalic anhydride (TBPA) are slowly added tothe DEG with stirring. 0.8 gram (0.014 mole) of KOH is then added to thestirred mixture followed by 152 grams (2.62 moles) of propylene oxide(PO). With continued stirring, the resultant mixture is heated to 60-65°C. at which point the mixture starts to exotherm and the temperature ofthe mixture increases to about 140° C. within about 5-10 minutes and thepressure in the reactor begins to rise.

External heating is removed at the onset of the exotherm and thetemperature and pressure are carefully monitored during the heat-upperiod. If necessary, cooling is applied to the reaction mixture and/orPO is vented from the mixture if the temperature exceeds 200° C. and/orthe pressure exceeds 45 psig (411 kPa). Once the reaction mixture hasreached its maximum exotherm temperature, the mixture is allowed to coolback down to 120° C. and then held at this temperature for 4 hours.Stirring is continued throughout the hold period.

At the end of the 4 hour hold period, the product is allowed to cool toan appropriate temperature for handling and, when the product hascooled, the reactor seal is released, after any excess pressure has beenremoved by venting the reactor vapor into a sulfuric acid scrubber ortrap. Stirring is now ceased and the acidity of the product is analyzed.If the acidity of the product is >0.25 mg KOH/g, additional propyleneoxide is added to the product and the product is heated at 120° C. foranother 0.5 hour and the acidity is rechecked. This operation isrepeated until the acidity of the product is <0.25 mg KOH/g.

Once the acidity of the product has reached 0.25 mg KOH/g or less, thecontents of the reactor are transferred into a 1 liter one-necked roundbottom flask. The flask is then placed on a rotary evaporator androtovapped at 75° C. at full aspirator vacuum to remove any volatiles.The resultant product is then removed and has the properties listed inTable 1.

Example 2

The process of Example 1 is repeated but with the reaction mixture beingcomposed of 200 grams (1.88 moles) of DEG and 1.6 gram (0.028 mole) ofKOH, the amounts of TBPA and PO remaining unchanged. A higher viscositydiester diol is produced having the properties listed in Table 1.

Example 3

The process of Example 1 is repeated but scaled up into a 5 liter piecepressure reactor and with the reaction mixture being composed of 990grams (9.32 moles) of DEG, 2881 grams (6.21 moles) of TBPA, 3.6 gram(0.063 mole) of KOH and 663 grams (11.43 moles) of PO. An intermediateviscosity diester diol is produced having the properties listed in Table1.

Example 4 (Comparative)

In this Example a route to making a diester diol of TBPA with DEG and POis described using toluene as a solvent.

Toluene (285 grams) is charged to a 1 liter one-piece pressure reactorequipped with a stirrer and 721 grams (1.6 moles) of TBPA and 29 gram(0.5 mole) of KOH are added to the reactor with stirring. Once the TBPAhas dissolved in the toluene, 234 grams (2.2 moles) of DEG and 160 grams(2.7 moles) of PO are added to the reactor. With continued stirring, theresultant mixture is heated to 55-60° C. at which point the mixturestarts to exotherm and the temperature of the mixture begins to rise.

The exothermic reaction is controlled using cooling as necessary so thatthe temperature of the mixture does not exceed 105° C. and, once thistemperature has been reached, the mixture is held at this temperatureunder stirring for 1 hour. Samples of the mixture are removed for acidnumber testing every hour and, once the acid number is withinspecification (<0.25 mg KOH/g), the reactor contents are heated undervacuum to start removal of the toluene solvent allowing the temperatureto increase to a maximum of 120° C. After vacuum distillation for 1hour, water is slowly added to the product mixture to improve tolueneremoval via azeotrope formation. After an additional 4 hours ofdistillation with water addition, sampling the product mixture isinitiated to test for toluene levels. Once the toluene concentration iswithin specification (<0.10%), the water injection is turned off butstripping is continued. After 1 hour of further stripping, sampling theproduct mixture is initiated to test for water levels. Once the waterconcentration is within specification (<0.15%), stripping isdiscontinued and the reactor contents are recovered. The resultantproduct has the properties listed in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Viscosity (K cps) 20-30 80-100 20-30  80-130 Acidity (mg KOH/g) 0.04-0.10 0.04-0.10 0.04-0.10<0.25 OH number (mg KOH/g) 225-240 220-225 225-240 200-235 Water (ppm)100-400 100-400 100-400 2000

Example 5

The process of examples 1 or 3 are repeated with the exception thatafter the DEG, TBPA and KOH are added, approximately 25-33% of the PO isadded over the course of 0.5-1 hour after which the reaction mixture isheld for 0.5 hour. During the hold time, the reaction begins to exothermwith temperatures reaching 50-90° C. After the hold, the remaining PO isadded over the course of 3-4 hours. The reaction will continue toexotherm during this period and can reach temperatures of 140° C. duringthis phase of the addition. After the addition is completed, thereaction is continued as described in Examples 1 and 3.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein.

We claim:
 1. A tetrabromophthalic diester diol composition comprising a diester diol having a formula

wherein n is from 1 to 5, wherein the tetrabromophthalic diester diol composition has a viscosity of about 20,000 to about 30,000 cps at 25° C. and consists of a diester diol composition obtained by a process comprising: (a) preparing a liquid reaction mixture comprising tetrabromophthalic anhydride, diethylene glycol, propylene oxide and between about 0.001 to about 0.05 mole potassium hydroxide per mole of tetrabromophthalic anhydride, said reaction mixture being substantially free of an organic solvent; (b) while agitating the reaction mixture, raising the temperature of the reaction mixture to between about 60° C. and about 65° C. to initiate an exothermic reaction and allowing the tetrabromophthalic anhydride to react with the diethylene glycol, propylene oxide and potassium hydroxide to produce a diester diol composition; and (c) terminating the reaction when the diester diol composition has an acid value equal to or less than 0.25 mg KOH/gm of diester diol composition.
 2. The tetrabromophthalic diester diol composition according to claim 1, wherein the reaction mixture prepared in (a) has a diethylene glycol:tetrabromophthalic anhydride mole ratio of about 1.5 to about 2.5:1.
 3. The tetrabromophthalic diester diol composition according to claim 1, wherein the reaction mixture prepared in (a) has a propylene oxide:tetrabromophthalic anhydride mole ratio of about 1.5 to about 2.0:1.
 4. A flame retardant polymer composition comprising (a) a flammable macromolecular material and (b) the tetrabromophthalic diester diol composition according to claim
 1. 5. The flame retardant polymer composition of claim 4 wherein the flammable macromolecular material is a polyurethane. 